Bearing sweep amplifier circuit



July 19, 1949. w. H. DOHERTY BEARING SWEEP AMPLIFIER CIRCUIT Filed Sept. 26, 1946 /N'VENTOR W. DOHERTY Patented July 19, 1949 UNITED BEARNG SVVEEP AMPLEIFIER (CIRCUT Application September 2.6, 1946, Serial No. 699,453

3 Claims. 1

This invention relates to bearing sweep amplier circuits for radar systems and the like. More particularly it relates to circuits for generating suitable balanced push-pull sweep voltages synchrcnized with an exploratory element, the phase of which sweep voltages can be conveniently and precisely adjusted to bring the sweep voltages into exact phase-coincidence with the exploratory element.

Circuits of the invention are of particular value in connection with radar systems of the type in which a sector in space is recurrently scanned by a highly directive or beam antenna. The sector scanned usually comprises an angle of from l5 to 30 degrees, though the principles of the invention are readily applicable to any size of scanning angle. The sweep'voltages are employed of course in the normal types of radar to deilect the ray of a cathode ray oscilloscope in synchronism with the sweeping motion of the highly directive beam of the antenna. Simultaneously the ray of the oscilloscope is usually deected in a second direction at right angles to the rst mentioned sweep, to portray a second dimension of the eld being scanned such, for example, as range, in which case the indication provided is known as a class B presentation.

In radar systems of this general type in the prior art it has been customary, in adjusting the sweep phase to Icoincide with the antenna bearing, to require a mechanical adjustment of some portion of the bearing indicating apparatus directly associated Vwith the antenna scanning mechanism. The present invention avoids this necessity and substitutes for mechanical adjustment a simple and precise electrical control means which can be located at any convenient point in the radar system. This is a distinct advantage in radar systems employed on aircraft or on shipboard where the antenna system may be mounted in a relatively inaccessible position.

The ldistinctive feature of the circuits of the invention comprises a balanced electronic sweep circuit controlled by a sine wave input. The sine wave input is derived by combining with one phase of a two-phase sine wave generator, driven by the antenna scanning mechanism, a controllable amount of the second phase of thev generator. By this means a precise and convenient control which may be eected at any desired station of the radar system `is provided.

A principal object of the invention is therefore to provide a precise and convenient means for controlling the phase of the bearing sweep of a sector-scanning type4 of radar system.

Another object is to provide a bearing sweep circuit the phase control of which can conveniently be located at a point remote from the antenna system of a sector-scanning type of radar system.

Other and further objects will become apparent during the course of the description hereinunder of a specific illustrative embodiment of the invention and from the appended claims.

The nature of the invention will be more readily understood from the following detailed description of a speciflc illustrative embodiment of the invention taken with the accompanying drawing in which the gure shows in schematic diagram form a system embodying the principles of the invention.

In more detail in the figure, the combination of reector 3G and radiating system 32 comprises a highly directive beam antenna system. Reflector 3i! is preferably parabolic in form and is a sheet or mesh of conductive material. Radiating system 32 is placed substantially at the focal point of reilector 3l) and can be either a simple dipole antenna, or an array of dipole antennas or a wave guide radiating structure arranged to direct energy toward the reector'Sll. The reflector, of course, focusses energy emanating from radiator 32 into a highly directive beam. Likewise it focusses .received energy, reflected from objects upon which the beam impinges, upon the radiator 32.

' As in conventional radar systems, well-known to those skilled in the art, pulse transmitter lil recurrently energizes radiator 32 with high power short pulses of energy, spaced suiiciently in time to permit the receipt of reections of each pulse before the emission of the next successive pulse.

TR box 38 functions to protect receiver 152 during the transmission of high power pulses by substantially short-circuiting the input to the receiver during the high power pulses. However, it instantaneously removes the short-circuit upon the cessation of each high power pulse thus conditicning the receiving circuit for the reception of the relatively weak reflections received between successive transmitted pulses. Receiver 62 detects and amplies the reflected pulses and transmits them to the amplitude control anode 48 of the cathode ray oscilloscope 4B causing a momentary brightening of the ray upon the receipt of each reilected pulse.

Through the medium of a. motor equipped with a reduction gear drive 34 and a reciprocating mechanism 35, the antenna system 30, 32 is caused to scan, by way of example, a sector of 15 degrees at a rate of ve times per second (double sweep). Lead 3l makes connection through a slip-ring or other appropriate electrical connection, many forms of which are well-known in the art, to radiator 32, thus maintaining the'desired connection between radiator 32 and units 38, 4I), 42.

The motor, the reduction gearuassociated therewith and the reciprocating mechanism can be of any of the numerous appropriate forms wellknown in the art.

Unit 3d also drives at the same rate (5 cycles per second), a two-phase Vsine wave generator 35. The voltages generated by unit 36 are employed in the circuit including vacuu tube lill, phase 1 being connected across resistance 3 and phase Z being connected across potentiometer 2, theresistance and potentiometer being connected in series as shown in the drawing. The voltages of the two phases of generator 36 are in quadrature relation i. e.,V one'is displaced 90wdegrees in phase with respect to the other. The generator is originallyv assembled so thatphase l is nearly n phase with the scanning' cycle of antenna 3B, S2. Potentiometer 2 permits the addition :to phase l oi' a precise amount of the voltage developed in phase 2. The eiective phase ofthe sine wave applied to control anode I, A'of double triode vacuum tube 6D, is therefore the vector sum of the voltage of phase livith a small portion of the voltage of phase 2 added4 in quadrature therewith. It is obvious that this arrangement provides a precise and convenient means for adjustingrthe phase of the eletive sine w'a've input to grid I of tube 60. n Y s Vacuum tube 69 is a cathode-coupled, phase= inverting amplifier., Direct current gridbiascs lfor the grids l and 4 of this amplifier are derived from the voltage divider -consisting of resistance fi, potentiometers 5 and 6, and rsistances 1, I8

and I9. A Y y n Y In accordance with cominon practice for electronic control circuitsI requiring relatively high voltages the mid=plointwofrthe voltage supply is grounded so that the effectivevoltag'e to ground from the points of highest voltage Ais out in half. Because of this we nd at terminals@ a positive voltage of 300 volts and at t'erninai 66 a negative voltage of acc vous'. The operation ofthe overall circuit, however, is obviou'slyfsiibstantlally that which would obtain, were a 600=volt source 'eini ployed. The negative terminal of the SOO-volt source connected lto terminal 64 (fornormal operation) is of course grounded, as is also the positive terminal of the 30G-'volt sure connected to terminal 66 (for normal operation). vThis ari rangement of voltages also obviously reduces the effects of distributed capacity to groundk throughoutthe circuit. Y Y n n Y The double triode Vacuum tuem ifunotins as an amplifier to increasethe amplitude of` the input sine wave to the desired leV'el. Also ys inr'zerthe cathode resistor 8 which is common toboth halves of tube 60 is not bypassed, the Cathode voltagin likewise a sine wave which is in phasewithlthe wave introduced at control anode I.V Therefore at the output terminals of plates 2 and 5, two sine waves are produced which are of equal amplitude but displaced inrphase by 180 degrees from each other. As isV well-known to Ythose skilled in the art, this ltype of balanced sweep wave coit'ribtes substantially to the maintenance Vof' `fidelity of focus of the ray over the entire sweep.Y The direct current level at which the output sweep' waves operate is controlled bythe sweep bias potentiometer 5, which adjusts the grid bias of both con- 4 trol anodes I and 4 of tube 6D. To insure that both output waves operate at the same direct current level, the sweep centering potentiometer G provides an additional independent means for adjusting the bias on control anode 4 of tube 6B.

Capacitors 2|, 22 and 23 reduce the distortion of the live-cycle sine wave which might result from the introduction of extraneous higher freouencies, for example, by cross-talk with other circuits of the radar system or with other electrical circuits in the vicinity.

The two five-cycle bearing-sweep voltages are applied to the control anodes I and 4, respectively, oi V the cathode-follower double-triode vacuum tube 62. The output voltages from this tube are of course taken from the cathodes 3 and E of tube 62 and are applied to the horizontal derlecting plates 50 of the cathode ray oscilloscope 46. The cathode-follower stage is employed for the usual purpose of providing a low-impedance output and permits the use of low impedance cables toconnect to the oscilloscope. A number 'of .Oscilloscopes can be operated in parallelfrom tliis source of bearing sweep voltage and can be distributed as desired, at numerous observation points some of which are usually remotely located with respect to the radar system.

Resistors 9 and I0 serve to isolate their respective anodes 5 and 2 from each other and contribute the varying voltage drops which duplicate the wave impressed upon control anode i of tube 60. K

Range sweep generator 44, actuated by pulse energy from pulse transmitter 40, is connected to vertical deecting plates 52 of oscilloscope 46 and serves to deect the rayvertically after each transmitted pulse Vso that the indication corresponding to any particular, received reected pulse will appear at a vertical distance from the base line of the oscilloscope screen corresponding to the distance of the object from which the reflection is received. Y

Numerous other circuits embodying the prinepies ci the invention can be readily devised by those skilled in the art without departing from the spirit of the invention, the scope of which is defined in the following claims.

What is claimed is:V l l 1. A bearing sweep generator circuit for use in -radar-systeins of the type which scan an area with 'a beam antenna said circuit comprising a two-phase sine wave generatordriven in synchronism with the scanning motion of the radar system beam antenna, the phases of said sine wave generator being'` in quadrature relation, a double triode vacuum tube amplifier of the cathodeecoupled phase-inverting type having an in- 'put control electrode and means for impressing on said last stated control electrode the full voltage of one phase of said sine wave generator in series with a selectedadjustable portion only of the'volta'ge of said other phase of said generator whereby a pair of balanced sweep voltage waves synchronized with the scanning motion of theV radar antenna and subject to convenient precisely adjustable phase alignment with said scanning motion can be obtained.

2. In a radar systemwhich includes a recurrently scanning beafnantena, means for producing a sweep wave voltage in phase with the scan-'- ning motion of said antenna which comprises means for generating two voltage waves in quadrature relation having definite phase relations With respect to the lSifzflnillg notil of Saidantenna and inea'ns for combining one of said voltage waves with a controlled amount of the other of said voltage waves to provide a third voltage wave the phase of which can be precisely adjusted to an in phase relation with the scanning motion of said antenna.

3. Means for producing a voltage Wave which can be precisely adjusted to an in phase relation with a recurrently scanning mechanism which comprises means for generating two voltage waves having a substantial phase diierence between them, means for driving said generating means in synchronism with said scanning mechanism and means for combining one of said two voltage waves with a controllable portion of the other of said two voltage waves to obtain a third voltage wave which is precisely in phase with the motion of said scanning mechanism.

WILLIAM H. DOHERTY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,150,265 Conover Mar. 14, 1939 2,421,747 Engelhardt June 10, 1947 2,427,905 Fyler Sept. 23, 1947 

